Packaged current sensor integrated circuit with exposed cooling pad

Some conventional current sensors are positioned near a current-carrying conductor to sense a magnetic field generated by a current through the conductor. The current sensor generates an output signal having a magnitude proportional to the magnetic field induced by the current through the conductor.

According to one aspect of the present disclosure, a current sensor integrated circuit package. In some embodiments, the package includes a primary conductor having an input portion into which a current flows and an output portion from which the current flows, a plurality of secondary leads, and a semiconductor die disposed adjacent to a top surface of the primary conductor and positioned on an insulator portion. In some embodiments, at least one magnetic field sensing element is supported by the semiconductor die. In some embodiments, the package includes a package body comprising a first portion enclosing the semiconductor die and a first portion of the primary conductor and a second portion enclosing an elongated portion of the plurality of secondary leads, wherein a second portion of the primary conductor is exposed. In some embodiments, a pad is secured to the package body and a pillar extends from the primary conductor to the pad.

According to one aspect of the present disclosure, a portion of the pad extends beyond a periphery of the package body. In some embodiments, the second, exposed portion of the primary conductor comprises the input portion of the primary conductor and the output portion of the primary conductor. In some embodiments, the portion of the pad extends over either the input portion of the primary conductor or the output portion of the primary conductor. In some embodiments, the pillar is disposed between the portion of the pad that extends beyond the periphery of the package body and the second, exposed portion of the primary conductor.

As used herein, the term “magnetic field sensing element” is used to describe a variety of electronic elements that can sense a magnetic field. The magnetic field sensing element can be, but is not limited to, a Hall effect element, a magnetoresistance element, or a magnetotransistor. As is known, there are different types of Hall effect elements, for example, a planar Hall effect element, a vertical Hall effect element, and a Circular Vertical Hall (CVH) element. As is also known, there are different types of magnetoresistance elements, for example, a semiconductor magnetoresistance element such as Indium Antimonide (InSb), a giant magnetoresistance (GMR) element, for example, a spin valve, an anisotropic magnetoresistance element (AMR), a tunneling magnetoresistance (TMR) element, and a magnetic tunnel junction (MTJ).

The magnetic field sensing element may be a single element or, alternatively, may include two or more magnetic field sensing elements arranged in various configurations, e.g., a half-bridge or full (Wheatstone) bridge, configured for single-ended or differential sensing. Depending on the device type and other application requirements, the magnetic field sensing element may be a device made of a type IV semiconductor material such as Silicon (Si) or Germanium (Ge), or a type III-V semiconductor material like Gallium-Arsenide (GaAs) or an Indium compound, e.g., Indium-Antimonide (InSb). A coil may also be used to sense magnetic fields, which may be referred to as inductive sensing. Using a coil to sense a magnetic field is more typical as the frequency of the magnetic field to be sensed increases.

As is known, some of the above-described magnetic field sensing elements tend to have an axis of maximum sensitivity parallel to a substrate that supports the magnetic field sensing element, and others of the above-described magnetic field sensing elements tend to have an axis of maximum sensitivity perpendicular to a substrate that supports the magnetic field sensing element. In particular, planar Hall effect elements tend to have axes of sensitivity perpendicular to a substrate, while metal based or metallic magnetoresistance elements (e.g., GMR, TMR, AMR) and vertical Hall effect elements tend to have axes of sensitivity parallel to a substrate.

As used herein, the term “magnetic field sensor” is used to describe a circuit that uses a magnetic field sensing element, generally in combination with other circuits. Magnetic field sensors are used in a variety of applications, including, but not limited to, an angle sensor that senses an angle of a direction of a magnetic field, a current sensor that senses a magnetic field generated by a current carried by a current-carrying conductor, a magnetic switch that senses the proximity of a ferromagnetic object, a rotation detector that senses passing ferromagnetic articles, for example, magnetic domains of a ring magnet or a ferromagnetic target (e.g., gear teeth) where the magnetic field sensor is used in combination with a back-biased or other magnet, and a magnetic field sensor that senses a magnetic field density of a magnetic field.

Referring to the various views of, a packaged current sensor integrated circuit (IC)includes a primary conductorhaving an input portioninto which a current flows, an output portionfrom which the current flows, and an exposed portion(shown in the bottom views of). A semiconductor dieis disposed adjacent to the primary conductorand is positioned on an insulator portion. At least one magnetic field sensing element,is supported by the semiconductor die. A package bodyencloses the semiconductor dieand a portion of the primary conductorand has an upper package body surfacea lower package body surfaceand side package edges,.

A padis secured to the package body. The padmay be secured to the upper package body surfacethrough a non-conductive adhesivedisposed between the padand the upper package body surface

A pillarextends from the primary conductorto the pad. The pillarcan be attached to the primary conductorthrough soldering or welding.

The padand pillarcool the packaged current sensor IC. The pillarprovides a low heat resistance path for dissipated heat to flow to the pad, rather than to the semiconductor die. The heat is then dispersed out of the packaged current sensor ICby the pad.

The pillarand padcan be comprised of various materials selected for heat conductivity and other factors. In an example embodiment, the pillarand padare comprised of copper. It will be appreciated by those of ordinary skill in the art that the pillarand the padmay or may not be comprised of the same material.

Additionally, the padcan provide high frequency stray-field shielding. Conductive material creates an eddy current that acts as a shield, accordingly the material the padis made of may provide stray field shielding. The padprovides interference immunity against external varying magnetic fields via the eddy current induced in the material the padis made of. The amount of interference immunity may be determined based on: the properties of the material the padis made of; the dimensions of the pad; and the frequency and strength of the external magnetic field. The padmay comprise a ferrous material or nonferrous material, which shield against magnetic fields that may be generated. Nonferrous material, such as aluminum or copper, can provide a higher interference immunity. Example ferrous materials include materials such as iron or nickel.

A secondary lead, such as leadhas an exposed portionthat is spaced from the exposed portionof the primary conductorby an isolation distance “d” (shown in the views of). A lead frame(labeled in) includes the primary conductorand one or more secondary leads (here a plurality of secondary leads-).

The example current sensor IChas secondary leads,In other embodiments, in which fewer than the illustrated six leads are required or more than the illustrated six leads are required for providing more power, ground, output signals, a fault signal, or other input and output pins, there may be fewer or more than six secondary leads. Wire bonds,connect the dieto the secondary, or signal leads,,respectively, as shown in the view of. In an embodiment, one or more secondary leadscan be connected to dieusing two or more wire bonds. This may be advantageous when a potential for higher current exists in the operation of the integrated circuit, such as for a power or ground connection to die.

Secondary leads-can be elongated from a first end adjacent to the primary conductorto the exposed portion-respectively, and thus, can be described as having an elongated portion. Secondary leads-can have a substantially constant thickness “t” (labeled in).

Creepage refers to the shortest distance between primary and secondary conductors along a surface of any insulation material common to both parts, such as the lower surfaceof the package bodyoutside of the package. The isolation distance “d” between the exposed portionof the primary conductorand the exposed portion-of any secondary lead-respectively, provides the creepage distance and can be at least 2.0 mm.

The package bodyhas a first portionenclosing the semiconductor dieand a portion of the primary conductorand a second portionenclosing elongated portion-of the plurality of secondary leads-The first portionof the package bodyhas a first width “W” configured to expose the input portionof the primary conductor and the output portionof the primary conductor and the second portionof the package bodyhas a second width “W” between a first side edgeof the package body and a second side edgeof the package body that is larger than the first width. The padmay be secured to the first portionof the package body, the second portionof the package body, or to both the first portionand the second portionof the package body.

The exposed input portionof the primary conductorand the exposed output portionof the primary conductoreach can have a length “L” of at least 0.5 mm. In some embodiments, the exposed length can be between 0.5 mm-1.5 mm. The exposed input portionof the primary conductor and the exposed output portionof the primary conductor are configured to accept one or both of a clamp or a test probe.

Lead framecan be stamped from a copper sheet and can be relatively thick (e.g., at least 15 mils thick) in order to support high current (e.g., 200 amps) applications. In lower current applications, more standard lead frame thicknesses, such as on the order of 8 mils or 10 mils can be used. Alternatively, lead framecan include interconnected metal layers as may be part of a so-called molded interconnect substrate (MIS) that includes a pre-molded structure with one or more layers, with each layer configured with plating or interconnects to provide electrical connections in the package.

The primary current conductorcan include die attach portions,and a current path portionbetween the die attach portions. The primary conductorsupports insulator, or insulator portion, and semiconductor die. Die attach portions,can alternatively be referred to as die attach pads or paddles. Diesupports at least one magnetic field sensing element, and, in an example embodiment, supports at least two magnetic field sensing elements,. The diecan also support circuitry to amplify and otherwise process signals from the magnetic field sensing elements,and provide an output of the current sensor integrated circuit. As current flows through the primary conductor, a magnetic field is generated and sensed by magnetic field sensing elements,. In some embodiments, each element,is comprised of a plurality of elements, such as four, as may be coupled in a bridge configuration.

In embodiments, the input portionof the primary conductoris exposed from the first side edgeof the package bodyand the output portionof the primary conductoris exposed from the second side edgeof the package body that is substantially parallel with respect to the first side edge of the package body.

A portion of the padcan extend beyond a periphery of the package body. For example, the padcan extend beyond a periphery of the first portionof the package bodytowards the input portionthe output portionor both the input portionand the output portionof the primary conductor. In, the padextends beyond the first portionof the package body towards the input portionof the primary conductor.

The pillaris disposed between the portion of the padthat extends beyond the periphery of the package bodyand the primary conductor. The pillaris disposed between the padand either the input portionor the output portionof the primary conductor. In, the pillaris disposed between the padand the input portionof the primary conductor. The pillaris positioned on one side of the primary conductor, accordingly it will not disrupt the current measurement of the packaged current sensor ICby diverting current from the conductor.

The input portionof the primary conductorhas a reduced area edgeand the output portionhas a reduced area edgeBy reduced area edge it is meant that the edge surface has a reduced surface area as compared to a flat edge. Each example reduced area edgehas a notch between edge ends, as shown. The reduced area edgesprovide tie bars which, during fabrication, are connected to like edges of primary conductors of adjacently fabricated packages. In other words, multiple current sensor integrated circuits are fabricated from a single lead frame (couped together by tie bars in the form of the reduced area edges) and are singulated along the side edges,of the package bodythrough the reduced area edges

Providing primary conductor edgesalong which the package is singulated (i.e., the connecting tie bar area) with a reduced area (i.e., as opposed a solid edge of a width “w” that needs to be cut) reduces the force required by the singulation process. For example, in the case of punching to singulate, the force required to punch through the reduced edge area is less and therefore, the IC package experiences lower stress and wear on the punch tool is reduced.

Reduced edge areasare spaced by less than or equal to the width Wbetween the first side edgeof the package body and a second side edgeof the package body so that edge areadoes not extend beyond side edgeand edge areadoes not extend beyond side edge. This arrangement advantageously prevents the IC packages from jamming in the tube during testing.

The elongated portionof the secondary leadsandrespectively, is offset with respect to the exposed portionof the respective secondary lead in a direction of the package height or, in other words, the secondary leads-are offset with respect to the exposed portions-in the direction of a thickness “t” as shown (see). A typical lead thickness “t” can be on the order of 0.5 mm. In embodiments, the dimension of the offset of the secondary leads-can be on the order of 0.25 mm. However, it will be appreciated by those of ordinary skill in the art that a smaller offset dimension, such as on the order of 0.1 mm, or a larger offset dimension are possible. With this arrangement, achieving a desired creepage distance can be facilitated by providing the secondary leads-with an offset elongated portion-that is thereby encapsulated by the package body. In other words, by offsetting the secondary leads-in this manner, the bottom surface of the elongated portion-is encased by the mold material of the package body, resulting in the creepage distance “d” extending between the exposed portionof the primary conductorand the exposed portions-of the secondary leads-Notably, this offset arrangement of secondary leads can achieve the same creepage as using secondary leads that have a thinned elongated portion formed by of a half etch process but can alleviate manufacturing challenges associated with half etch processing of long leads since such relatively long half etched secondary leads can be prone to bending.

The illustrated secondary leads-can have a substantially constant thickness “t” (labeled in) or can have a thinned elongated portion formed by of a half etch process. In embodiments, the isolation, or creepage distance “d” is at least 7.2 mm and can be at least 8.0 mm. With a creepage distance of at least 7.2 mm, reinforced isolation according to a standard, such as IEC60664, is achieved for basic working voltages>1000 VRMS. In some embodiments, lower voltage isolation requirements may exist and the isolation distance “d” may be at least 1.0 mm, 2.0 mm, or 4.0 mm to meet certain isolation requirements in different applications.

Clearance refers to the shortest distance between conductors of differing voltage levels, such as between primary and secondary conductors, through an insulating material, such as air outside of the package or through an insulating material inside or outside the package.

Increased clearance distance can be facilitated by the insulator portionextending beyond an edge, such as a top edgeof the primary conductoras shown in, since such extended insulator portion increases the clearance distance between the lower voltage level semiconductor dieand the higher voltage primary conductor. The insulator portionextends beyond edgeof the primary conductorin order to provide voltage isolation. In general (although the illustrated insulator portionextends beyond the primary conductor edgein an example embodiment), the insulator portionneed only extend beyond the dieby at least 200 microns and preferably by 400 microns. In an embodiment, the insulator portionmay extend beyond the edgeof the primary conductorby at least 50 microns, and in another embodiment the insulator portionextends beyond the edgeof the primary conductorby at least 375 microns. An embodiment may have the insulator portionnot extend beyond the edgeof the primary conductorwhere the other dimensions provide sufficient electrical isolation for the desired application.

From the bottom views of, it can be seen that each of the secondary leadshas an exposed portion,respectively, on the bottom of the package. Further, lower surfaceof the primary conductoris also exposed on the bottom of package. In use, exposed surfaceof the primary conductormay be connected to a circuit board or other substrate.

Current path portionof the primary conductorbetween the input and output portionscan be narrowed, as shown, to concentrate the magnetic field in the vicinity of the sensing elements,. Die attach portions,are configured to enhance mechanical securing of the mold materialto the lead frame.

The magnetic field sensing elements,are positioned off of or to the side of the current conductor portionso that the magnetic field generated by the current flowing in the current conductor portionhas a directional component that is perpendicular, or in an embodiment near perpendicular (e.g., in some embodiments within +/−20 degrees of perpendicular and in other embodiments more than +/−20 degrees), to the diesuch that planar Hall effect elements may be used for magnetic field sensing elements,. If the magnetic field sensing elements,are Hall effect elements, one Hall effect element may be designed to have a positive voltage output when the magnetic field sensed is out of the die(where for clarity “out” is the direction away from the current conductor portion), and the second Hall effect element may have a negative voltage when the magnetic field sensed is out of the die. Various processing circuitry is responsive to signals from the magnetic field sensing elements for generating an output signal indicative of the current through the current conductor portion. Such processing circuitry can include, but is not limited to an amplifier, and in some embodiments a differential amplifier, supported by the integrated circuit dieand configured to generate a signal indicative of the difference between the two Hall effect element output voltages. Using the difference between the two magnetic field sensing element output voltages when they are Hall effect elements allows for the integrated circuit to reduce or eliminate the effects of external magnetic fields that are not a result of current through the primary current path, including the current conductor portion(i.e., stray magnetic fields). In other embodiments, the magnetic field sensing elements, or a magnetic field element may be positioned on dieover the primary current conductor portionto sense a magnetic field with a component parallel to the surface of die. In a case where the magnetic field component to be sensed is parallel to the surface of the die, a vertical Hall effect element or a magnetoresistance element such as a GMR, TMR, or AMR element may be used.

Accordingly, the magnetic field sensing elements,are positioned off of or to the side of the current conductor portionso that the magnetic field generated by the current flowing in the current conductor portionhas a directional component that is perpendicular, or near perpendicular, to the diesuch that planar Hall effect elements may be used. Various processing circuitry is responsive to signals from the magnetic field sensing elements for generating an output signal indicative of the current through the current conductor portion. In other embodiments, the magnetic field sensing elements may be positioned over the primary current conductor portionto sense a magnetic field with a component parallel to the surface of die, in which case a vertical Hall effect element or a magnetoresistance element such as a GMR, TMR, or AMR element may be used.

Dieis supported by one or both of the die attach portions,and is positioned over the insulator portion. Diemay be attached to the insulator portionby a non-conductive coating (not shown), such as a wafer backside coating (WBC) or a non-conductive epoxy or a dispensed die attach material, die attach film, or other material. The insulator portionis attached to die attach portions,. Alternatively, diecan be attached to the insulator portionby a conductive material as may reduce the effects of partial discharge from voids in the die attach material. Diemay be attached to die attach portions,by insulator portionwhere the insulator is a dielectric tape, for example a Kapton® or other insulating tape with a layer of adhesive on one side of the tape or on each side of the dielectric tape layer. In another embodiment, an epoxy die attach material, a die-attach film (DAF), or an insulating coating material may be applied as the insulator portionin place of the tape. Further, thin fiberglass, glass, ceramic or other thin insulating layers can be used instead of tape. Aspects of insulator portioncan be the same as or similar to insulation structures described in U.S. Pat. No. 10,753,963, issued on Aug. 25, 2020, entitled “Current Sensor Isolation” and hereby incorporated herein by reference in its entirety. In manufacturing, if two layers of wafer backside coating are used, a first wafer backside coating layermay be fully cured (or partially cured if only one layer of a wafer backside coating is used) before a second layer of wafer backside coating is partially cured (also known as B stage cured) to attach dieto insulator portion.

In another embodiment, diemay be attached to the insulator portionby other materials, including but not limited to a non-conductive die attach epoxy, or a tape. Multiple layers of wafer backside coating, tape, DAF and non-conductive epoxy may be used for electrical isolation. A combination of wafer backside coating, tape, DAF, or non-conductive epoxy may be used to achieve electrical isolation and attachment to the die attach portion,.

The insulator portioncan provide a second layer of isolation between the primary conductorand wire bonds-and secondary leads-which allows a thinner package than if a 0.4 mm distance were required. It will be appreciated that the isolation distances can be readily varied by stretching or shortening the length of the enclosed portion of the secondary leads in order to achieve a desired isolation voltage.

The insulator portioncan extend beyond one or more edges, such as a top edgeand/or a side edgeof the primary conductorin the direction of, or from the side of the primary conductor towards, the secondary leads-. For example, in embodiments, the insulator portionmay extend beyond the top edgeof the primary conductorin the direction of the secondary leads-by at least 0.1 mm, 0.2 mm, or 0.4 mm depending on the voltage isolation requirements.

According to an example manufacture process, lead frameis formed with primary current conductorand secondary signal leads-following which insulation portionis applied to the primary conductor. The lead framemay be stamped from a single sheet of copper. The pillaris disposed on the lead framein a subsequent fabrication step. The insulationmay comprise one or more of a dielectric tape, an insulating epoxy material, or a piece of insulating material including but not limited to alumina or glass substrate material. The integrated circuit dieis then attached to the subassembly. Attachment of the diecan include, but is not limited to, use of a wafer backside coating material, a tape attachment material, and/or an insulating epoxy material, which may also be referred to as a non-conductive epoxy material.

The integrated circuit dieis electrically connected to the signal leads-such as with wire bonds-respectively. Other electrical connections, including flip-chip assembly methods, may be used provided they meet the isolation requirements of the application. Thereafter, a mold material is applied to the subassembly including the lead frame, integrated circuit die, and wire bonds-in order to form package body.

After the mold process that forms the package body, the padis secured to the package body. In order to secure the pad, adhesiveis disposed on the package body, the padis disposed on the adhesive. Alternatively, or in addition to the adhesive, the padmay be disposed in the package bodyso as to secure the padto a part of the package body. Accordingly, a portion of the padmay be disposed in the package bodysuch that a portion of the package bodymay surround or encompass the pad. The padis disposed such that it contacts the pillar. Following, the packages are cut, or singulated, with a process such punching, to form individual integrated circuit packages. Singulation results in the above-described configuration in which the primary conductor does not extend beyond the molds. As described above, advantageously, the reduced area edgesreduce the force required for punch singulation and thereby reduce the stress on the resulting IC packages and wear on the punch tool.

Other steps may follow manufacturing which include, but are not limited to a final test procedure, or programming the integrated circuit package. In the case of a current sensor integrated circuit package, there may be a test step and maybe programming of the integrated circuit die at the integrated circuit package level, and then a second test and programming may be performed, for example, when the current sensor integrated circuit package is applied to a printed circuit board or other assembly where the current sensor integrated circuit package is used. This second programming after assembly of the current sensor integrated circuit package onto a PC board or other assembly, allows a more accurate measurement of the current to be made as other influences such as PC board currents can be accounted for in the current sensor integrated circuit. As noted above, provision of cutouts,in the side edges,of package bodysuch that the reduced area edgesof the primary conductordo not extend beyond the package body edges,facilitates testing by reducing jamming of the package in the tube used for testing.

Manufacturing steps, including test steps, can be facilitated by the package body design with the first portionhaving a width Wconfigured to expose the input portionof the primary conductor and the output portionof the primary conductor. As noted above, the exposed input portionof the primary conductorand the exposed output portionof the primary conductoreach can have a length of at least 0.5 mm. In some embodiments, the exposed length can be between 0.5 mm-1.5 mm. The exposed input portionof the primary conductor and the exposed output portionof the primary conductor are configured to accept one or both of a clamp or a test probe.

Referring to, an alternative packaged current sensor integrated circuit (IC)may be similar to packaged current sensor ICand thus may include a primary conductor(that may be the same as or similar to primary conductor). A semiconductor die(that may be the same as or similar to semiconductor die) is disposed adjacent to the primary conductorand is positioned on an insulator portion(that may be the same as or similar to insulator portion). A package bodyencloses the semiconductor dieand a portion of the primary conductor. The package bodyhas an upper package body surfaceand a lower package body surface

Current sensor ICdiffers from current sensor IC() in that padis partially embedded in the upper package body surfacerather than attached to the upper package surfaceas in. By partially embedded, it is meant that the padis disposed in the package bodyin a recessalong the upper package body surfaceThe recessextends along a portion of the package bodyalong the upper package body surfacesecuring the padin the package body. Accordingly, the pad, while secured in the package body, does not contact the semiconductor die, insulator portion, or primary conductor. During the manufacturing process of forming the package body, described above, the padmay be molded into the package body. A pillar(that may be the same as or similar to pillar) extends from the primary conductorto the pad.

Referring to, an alternative packaged current sensor integrated circuit (IC)may be similar to packaged current sensor ICand thus may include a primary conductor(that may be the same as or similar to primary conductor). A semiconductor die(that may be the same as or similar to semiconductor die) is disposed adjacent to the primary conductorand is positioned on an insulator portion(that may be the same as or similar to insulator portion). A package bodyencloses the semiconductor dieand a portion of the primary conductor. The package bodyhas an upper package body surfaceand a lower package body surface

Current sensor ICdiffers from current sensor IC() in that padincludes one or more finsprotruding from the pad. The padis secured to the upper package body surfacethe finsextend away from the upper package body surfaceThe finsmay provide additional cooling, by providing additional surface area for heat transfer. A pillar(that may be the same as or similar to pillar) extends from the primary conductorto the pad.

Referring to, an alternative packaged current sensor integrated circuit (IC)may be similar to packaged current sensor ICand thus may include a primary conductor(that may be the same as or similar to primary conductor). A semiconductor die(that may be the same as or similar to semiconductor die) is disposed adjacent to the primary conductorand is positioned on an insulator portion(that may be the same as or similar to insulator portion). A package bodyencloses the semiconductor dieand a portion of the primary conductor. The package bodyhas an upper package body surfaceand a lower package body surfaceA padis secured to the package body.

Current sensor ICdiffers from current sensor IC() in that a pillaris disposed in the package body, as opposed to the pillardisposed between the portion of the padthat extends beyond the periphery of the package bodyand the primary conductoras in. The pillaris disposed on the primary conductoradjacent to the insulator portionand extends to the pad. The pillaris disposed near the output portionbut may be disposed near the input portionThe pillaris not in contact with the insulator portion.